1. Enzymes

2. Learning Objectives
Explain how chemical reactions affect chemical bonds.
Describe how energy changes affect how easily a chemical reaction will occur.
Explain why enzymes are important to living things.

3. Chemical Reactions
A chemical reaction is a process that leads to changes in the composition of matter.
Reactants are found on the left side of the reaction arrow, productions on the right
Chemical reactions do not create or destroy matter, they just change it.
During a chemical reaction heat can either be released or it can be absorbed.

4. An example reaction Energy-absorbing Can occur spontaneously
Requires more energy to get started
Reactants
Has a lower activation energy
Ask: Are these reactions energy-absorbing or energy-releasing?
Click to reveal the answer: energy-absorbing
Ask: Do these reactions occur spontaneously?
Click to reveal the answer: Occur spontaneously.
Click to reveal the statement: Requires more energy to get started
Ask: Which of these reactions requires more input of energy to get started?
Click to reveal the answer: blue
Click to reveal the statement: Has a lower activation energy
Ask: Which of these reactions has a lower activation energy?
Click to reveal the answer: red
Click to reveal the statement: Will proceed more quickly
Ask: Which of these reactions will proceed more quickly?
Introduce the term catalyst.
Will proceed more quickly

5. Enzymes lower activation energy and speed up chemical reactions of cells:

6. Enzymes speed up the cell’s chemical reactions by lowering energy barriers
Most reactions in living things require enzymes to help break bonds that hold them together.
Enzymes are proteins that act as biological catalysts which help to lower the activation energy of a given reaction.
The energy of activation is the amount of energy required to start a reaction.

7. Enzymes are specific for the reaction they catalyze
Every enzyme is unique and only fits a specific reactant (known as a substrate in enzyme catalyzed reactions)
The substrate fits into a part of the enzyme called the active site (like a key fits a lock)
Enzymes change shape to force a bond to be made or broken.

8. Active Site
The active site of the enzyme and the substrate have complimentary shapes.

9. Effects on enzyme activity
An enzyme’s shape is essential to its function.
Enzymes can be exposed to environments that cause them to lose their shape or denature – you can think of it as melting.
Enzymes are permanently damaged from:
High temperature
Salt concentration pH
Enzymes can lose their flexibility but not their shape. If temperature is too low, activity will stop but as they are warmed to appropriate temperature they will work again.